The use of mission-specific ensembles by occupants of aircraft and spacecraft has been well established. Depending upon the mission for which the ensembles are intended, they can take any of a wide variety of forms. While, for low-altitude missions (between, for example, altitudes of 10 thousand and 50 thousand feet), special breathing masks may be required, for high- altitude aircraft missions and space missions, pressurized suits are required. Below 10 thousand feet, no mask may be required at all, unless a chemically or radiationally contaminated atmosphere is expected.
There are three types of pressurized ensembles: full pressure suits, and partial pressure suits, and hybrid suits. Full pressure suits, which enclose the wearer's entire body, allow the pilot to remain at his chosen altitude, even following cockpit decompression. Partial pressure suits, which do not cover the wearer's extremities and have a separate non-pressurized helmet and visor and a breathing mask, give counter-pressure to the wearer's torso to aid the wearer's breathing. Partial pressure suits require the pilot to descend below 25,000 feet following any cockpit decompression in order to avoid physiological damage due to altitude sickness. Hybrid suits feature a full pressure helmet used with a torso-covering pressurized garmet.
Present full pressure suits operate at a pressure of 3.5 pounds per square inch differential (psid). There are several disadvantages associated with the use of such suits. For example, prior to takeoff, it is required that the wearer pre-breathe pure oxygen for sixty to ninety minutes. In addition, donning full pressure suits is slow and requires assistance, particularly because a full pressure suit weighs approximately 40 pounds.
On the other hand, some partial pressure suits are lightweight, can be donned rapidly without assistance, and are designed for use in environments in which full pressure suits are incompatible, especially those where quick response is required.
Both full and partial pressure suits can include, or be used with, equipment required for special purposes. Examples are anti-gravity garments needed in high acceleration environments and specialized filters needed in chemically or radiation-contaminated environments. Hybrid suits, incorporating some elements of full pressure and of partial pressure suits, are also possible.
In some situations, there may not be a need for an occupant to use a full ensemble. Examples of such situations are to use the craft to practice takeoffs and landings or to ferry the craft to another location, where a pilot need not wear anything more than a standard flight suit. Wearing an ensemble that exceeds the performance requirements of the mission at hand can be unnecessarily burdensome and may possibly lead to pilot fatigue and consequent errors.
At present, virtually all air- or spacecraft are mission-specific. The use of a pariticular craft for a wider variety of missions, some requiring full pressure suits for high altitudes, others requiring other partial pressure suits, requires that the craft be reconfigured with each new mission to support the newly-required ensemble. Reconfiguration is very expensive and time-consuming, so that it can be impossible in case a quick response is needed.
The control of the environment of such a suit can be sophisticated, employing anti-g valves, thermal, and communications systems. In addition, different missions can require breathing gas mixtures. Each suit type demands different controls and different breathing gas and temperature schedules.
It is desirable, therefore, to have a universal life support system able to function with a variety of mission-specific suits without requiring reconfiguration of the cockpit of the craft.